Talents, no. Talents represent that special ability and complement skills and define your character.
The +5% to the starting profile is a significant add in context of how skills grow in game through career advancement.
They are not cumulative in career advancement. Unfortunately, this is not called out in the rules very well.
Mentioned was Skill Mastery in comments above, this is a good example of how Talents are not "mastered," but inherent to the career first encountered or later found. Hardy is a birth Talent as is Night Vision. Hardy might be said you have or don't have and as you enter a new career that provides Hardy again, does it make you "more hardy"? I don't think so.
More context can be found in specifics: A Bone Picker may pick Hardy at character inception over Resistance to Disease and advance to Camp Follower. The choices for the Camp Follower are Hardy or Suave. Having taken Hardy in her Basic Career, Suave is left as the only option. It also means that the character may take Suave in Camp Follower to exit (100 XP). This is optional, per the Rules as Written.
Many Careers offer skill and talent choices. The Agitator career, for example, gives you the choice of the Coolheaded or Street Fighting talents. To start with you MUST take one of the two, otherwise you cannot complete the career.
However, before finishing your advance scheme, you may spend XP to gain these OPTIONAL skills and talents. As always, each skill or talent costs 100 XP. You don’t have to buy these skills and talents to finish the career, but you do have the option. As always, check with your GM before doing so.
Core Rulebook (US English, 1st printing), p. 28
I'll stipulate the oversight in the rules is subject to abuse. My arguments against stacking might cite: Night Vision. Do you become better at Night Vision? No. I think that the unwritten expectation is that adds to starting characteristics to the profile are one (1) time only, as are bonuses to skill checks, e.g., Menacing. The bonuses do not stack.
I will also cite Strike-to-Stun, as early as 2008, where this question was asked as well: Two rules questions.
Because of the lack of clarity I would not be surprised to find others with a contrary opinion, but lack of definition should not be assumed as "wiggle room."